Sanshirou's prospects for an adventure in his small island hometown are practically nonexistent, until a mysterious stranger invites him to play a game... Suddenly, Sanshirou is transported to an inverted universe to participate in BakéGyamon—a contest where monsters battle other monsters. During his journey, he encounters other players who have a specific motive for being there: to secure the wish granted to the victor. But how far can Sanshirou progress when the monsters he is paired with are merely a group of small mud balls?!